Thermal magnetic current by-pass



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THERMAL MAGNETIC CURRENT BT-PAss Filed Nov. 24, 1958 3 Sheets-Sheet 5 FE 2U.

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United States Patent O THERMAL MAGNETIC CURRENT BY-PASS, Carl E. Gryctko, Haddon Heights, NJ., and Kenneth Ball, Philadelphia, Pa., assignors to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Nov. 24, 1953, Ser. No. 775,862 2 Claims. (Cl. 20G-S8).

Our invention relates to circuit breakers in general and is more particularly directed to a novel construction for an actuating means for the shunting means which bypasses the bimetal 'time delay trip element of the circuit breaker upon the occurrence of a severe overload condition.

Molded case circuit breakers are provided with a time delay trip unit usually in the form of a bimetallic element and an instantaneous trip element which is in the form of a yoke armature combination. On the occurrence of an overcurrent, the deflection of the mimetal will be effective to delatch the cradle mechanism and on the occurrence of la fault current the magnetic yoke will be sufficiently energized to attract its armature thereby resulting in delatching of the cradle mechanism to effect contact disengagement.

It has been found that the bimetal will be permanently deformed if it is subjected to excessive currents. Some circuit breakers of the prior art have included circuits which shunt current so as to by-pass the bimetal upon the actuation of the instantaneous trip unit. In this way ythe bimetal is protected from excessive current from the moment that the armature is attracted by the yoke. However, the armature is of a substantial mass so that its operating time is not instantaneous.

lIt has also been found that upon Ithe occurrence of a short circuit condition the bimetal shunt circuit is not Aactuated by the instantaneous trip unit in a sufficiently short interval of time so as to prevent burn-out or distortion due to excessive heating in the case of a directly heated bimetal. The problem is particularly severe in circuit breakers having a low continuous current rating, hence a high resistance bitmetal.

This problem has in part been solved by providing a shunting circuit which is actuated by the bimetal itself as fully explained in copending application Serial No. 740,041 filed June 5, 1958, now Patent No. 2,989,605, entitled Bi-metal Actuated Bi-Metal Shunt with J. H. Leonard as inventor and assigned to the assignee of the instant invention. In the circuit breaker of the aforesaid copending application, the free end of the bimetal carries a contact which upon suicient deflection of the bimetal, 'engages a contact in a shunt circuit which is completed when the two contacts are in engagement. The shunt Vcircuit is not complete during normal heating of the bimetal but is closed when there is :over-heating at a time before burn-out or distortion set in. Thus the shunt does not carry current for an extended period of time but merely for some time less than it takes the circuit breaker to open after being hit by a short circuit or severe fault condition. The bimetal actuated shunt, in addition to its superior electrical qualities over that of the instantaneous trip operated shunt, offers the advantages of compactness and fewer number of parts.

The shunt comprises a member which is securely fastened `at one end and extends parallel to thc bimetal.

A contact is secured to the shunt at its free end'and is positioned to be engaged by a contact carried by the bimetal, at the free end thereof, when the deflection of the bimetal reaches a predetermined point. In order to prevent a reverse delleotion of the bimetal under extremely high current conditions, the shunt is constructed of a 3,096,413 Patented July 2, 1963 ICC yieldable material. However, the material is suiliciently resistant to deliection to prevent contact rebound and maintain contact pressure sutlicient to establish a low resistance juncture.

Thus, in choosing the material of the shunt it becomes necessary to comprise between the rrigi-dity necessary to prevent rebound and maintain contact pressure, and the yieldability necessary to prevent reverse deflection. This compromise has often resulted 4in excessive arcing at the shunt circuit contacts leading to a high resistance junction which introduces a high impedance into the shunt circuit.

The instant invention maintains the shunt circuit contact junction at `a low impedance by providing a magnetic means associated with the bimetal and its protective shunt. The shunt comprises a yieldable member and the magnetic means urges the shunt member toward the bimetal upon the occurrence of an over-current. Once the contacts of the shunt path have been closed, the magnetic means exerts a closing force to hold the contacts closed and help prevent contact blow-olf due to current flow through these contacts.

Accordingly, a primary object of the instant invention is to provide a novel shunting circuit for the thermal time -delay tripping element of a circuit breaker.

Another object of this invention is to provide a directly heated thermal time delay trip element and a shunt therefor which are both mechanically independent of the instantaneous trip device although both act on the same common tripper bar.

Still another object is to provide a bimetal actuated bimetal shunt, including associated magnet means, for the directly heated bimetallic element of an instantaneous trip unit of a molded case circuit breaker.

These as well as other objects of the instant invention shall become readily apparent after reading the following description of the accompanying drawings in which:

FIGURE l is a top view of a three pole circuit breaker, including my novel bimetal actuated bimetal bypass, with the cover removed.

FIGURE 2 is a side sectional view of the circuit breaker taken along line 2-2 of FIGURE l, and illustrates the operating mechanism after the circuit breaker has been tripped due to an overcurrent.

FIGURE 3 is a perspective view illustrating the meohanical independence of the time delay bimetal 'and its shunt from the instantaneous trip unit.

FIGURE 4 is ian end View of the overcurrent device.

FIGURE 5 is a side view of the novel bimetal actuated bimetal shunt.

FIGURE 6 is a view taken in the direction of the arrows 6-6 of FIGURE 5.

FIGURE 7 is a side elevation of the bimetal of the center phase and its associated shunt.

FIGURE 8 is a cross-section taken through line 8-8 of FIGURE 7 looking in the direction of arrows 8-8.

FIGURE 9 is a side elevati-on similar to FIGURE 7 illustrating a variation of this invention wherein a magnet is mounted to the shunt las well as ytoi the bimetal.

FIGURE l0 is a cross-section taken through line 10- 10 of FIGURE 9 (looking in the direction of arnows 10-10.

At the outset it is pointed out that the circuit breaker 10 to be hereinafter described is a three phase unit having substantially identical electrical elements for each phase. Thus, Ifor the sake of brevity and clarity only the center phase will be described so that a reference numenal followed by a capital letter such as B means that there is a corresponding element in the other two phases.

Referring first to FIGURES l and l2 showing a three pole embodiment of a `circuit breaker in which our invention can be adapted, the housing 20 of the circuit breaker 1t) is preferably made of a plastic substance and is provided with appropriate openings 21B and 22B through wlhich the circuit breaker terminals 25B and 26B, respectively, are substantially brought out of housing 20 to be engaged by the line terminals of the line to be protected. This circuit breaker may be of the type shown 'in U.S. Patent 2,673,9081to I C. Brumeld entitled Instantaneous Trip Circuit and assigned to the assignee orf the instant application.

The housing 20 :consists of two sections, a base 20a which is a section of the housing 20 on which the vanious components of the circuit breaker are mounted as here inafter described and a cover b Which completely closes the circuit breaker 10 by tightly engaging the base 20a.

Considering then this center phase B of the three pole circuit breaker 10, the circuit breaker terminal B rests against .an extending shoulder 28B of molding 20a. Shoulder 20B is perforated to receive threaded insert 29B ywhich eventually receives a bolt (not shown) to secure the line terminal (not shown) to circuit breaker terminal 25B. As previously mentioned, circuit breaker terminal 25B extends through opening `21B into base 20a. Circuit breaker terminal 25B lis shaped like an angle, one side 30B of the angle being used .to receive a line terminal (not shown), while the other side 31B is soldered or in any other way connected to a pigtail or conductor 35B.

Pigtail 35B is rigidly #secured t0 cross member 300B mounted to bimetal 38B at the calibration screw 43B. As best seen in FIGURES 3 through 6, the L-shaped thermal responsive means 38B has one lleg thereof positioned on top of the substantially U-shaped magnetic yoke 200. A screw 201 is passed through the leg of ixed shunt member 301B, through one leg of the bimetal 38B through magnetic yoke 200 into the molding 20a. Tlhus, the screw 201 secures both the bimetallic element 38B and the magnetic yoke 200 to [the base molding 20a and also serves to electrically connect the terminall 48B Ito the bimetallic element 38B. P'igtail 52B is soldered or otherwise secured to the diagonally extending tip 48B of shunt member 301B. Thus, a complete current path is provided ffrom the pigtail 52B to the terminal 48B and out the pigtail 35B to thereby form a single turn for the energization of the magnetic yoke 200.

A pivotally mounted shaft 203 mounted in bearings 204, 205 contains wire spring 206. A barrier plate 209 positioned Within appropriate recesses ot the groove in base molding 20a for the overcurrent device serves as a stop for one end of lthe wire spring 206.

The armature 211 is secured to the rotatably mounted shaft 203 at the area which contains the wire spring 206 and serves as a stop for the opposite end of this wire spring. It will be noted that the wire spring 206 may be mounted on either side of the armature 211 rather than being mounted yin the center as shown in FIGURE 3. With only one end of the spring 206 engaging rthe arrnature 211, it will not be necessary to reduce the crosssectional area of the shaft 203 to mount the spring. Thus, as best seen in FIGURE 5, the armature 211 is biased in va counterclockwise direction around the shaft 203 due to the Wire spring 206. The bottom ledge of the barrier 209 serves as a stop to elimit the counterclockwise rotation of the armature 211.

rIlne enlarged magnetic section 213 of the armature 211 is positioned above the prole faces 214 yand 215 of the magnetic yoke 200. On the occurrence of a faullt current, the single turn comprising the current How through the bimetal 38B will sufficiently energize the magnetic yoke 200 so that the portion 213 of the armature 211 will be attacted toward the pole faces 214 and 2-15. That is, the armature 211 will be rotated in a clockwise direction against the bias oit the wire spring 206. The protruding portion 21B of the armature 1211 will then be against the protrusion 60B of .the common tripper bar 65.

As willl be apparent, the countercl'ockwise rotation of 'the common tripper bar 65 will effect disengagement of 4 the latch 147B-152B to thereby elect disengagement of the cooperating contacts 7785.

llt will be noted that the movement of the armature 211 when attracted by the magnetic pole 200 is completely independent of the movement of the bimetal v38B and hence, clockwise rotation thereof will result in a hammer blow on the proitrusion 60B of the common tripper bar 65 to eect contact disengagement. The portion 66B of the common tripper bar 65 is positioned in alignment with the `adjustment screw 43B of the thermal element 38B. Thus, on the occurrence of an overcurrent, the bimetal 38B will deflect to the right in the conventional manner as seen in FIGURE 2, to thereby engage the portion 66B and cause counterclockwise rotation of the common tripper bar 65. It will be noted that when the circuit breaker `is tripped due to the occurrence of an overcurrent condition, the bimetallic element 38B will deect to the right and Iits movement willl be independent and unaffected by ythe .instantaneous magnetic trip means 200--21L The common tripper bar 65 provided at phase B as above noted has an extending member having portions 60B and 66B which are respectively engaged by the portion 216 of the armature 211 and the adjustment screw 43B of the bimet'al 38B.

The pigtail 52B to the fault current responsive means 38B and 211 is electrically connected to the arm 71B at the end 70B thereof. Movable contact arm 71B is pivoted by means of the pivot pin 72B engaging aligned openings 73B of the metallic f-rame or support 75B. Contact arm 71B is provided at its other end with a substantially rectangular shaped contact slab 77B. Contact slab 77B made of good conducting material is rigidly secured to contact arm 71B by means of a rivet 78B or in any other suitable way.

Stationary contact 80B consists of a rectangular section metallic member 81B having at the end nearer to contact arm 71B a stationary contact slab 85B rigidly secured to member 81B. Member 81B is secured to housing 20a of the circuit breaker through a screw 86B and a washer 87B. Stationary contact 80B is also provided with a terminal extension 26B an integral part of metallic member 81B, which extends for a portion 901B out of housing 20a to permit by means of screw means (not shown) for the connection of a line terminal to circuit breaker terminal 26. Stationary contact 80B is further provided with an anc extinguishing chamber B or are chute having a number of arc extinguishing plates 96B so that at the opening operation of the circuit breaker the arc existing between contact slab 77B `and contact slab 85B is extinguished before producing damage to the contact slabs 77B and 85B.

The operating mechanism of the circuit breaker, which forms no part of my present invention, is -described in the aforementioned U.S. Patent 2,673,908.

T-member B is provided at its upper portion 122B with a substantially rectangular extension 131B. Upper portion 122B of T-member 120B is slotted in its mid portion and provided with raised member 132B cut out from the upper portion 122B of T-member 120B which serves to be engaged by a plastic operating handle 135B for manually opening and closing the circuit breaker, as herein-after described. One leg `B of the V-shaped cradle 145B is shaped as shown in FIGURE 2 to engage a latch 147B. Latch l147B is provided with a slot 148B engaged by pin 150B around which latch 147B can rotate and can also have translational motion. Latch 147B is provided with a pointed end 151B latched under normal conditions by a latch surface 152B on the tripper bar 65.

Latch surface 152B is composed of a thin strip of vmaterial on tripper bar 65 supporting the latch 147B. The leg 157B of V-shaped member 145B is provided with a cylindrical hole engaged by a pivot pin 160B secured to the raised portion B of frame 75B. Leg 157B of V- shaped member 145B is provided at the bottom of the V with a shoulder extension 166B. Raised portion 165B of frame 75B is provided with an opening :through which passes contact slab 77B of movable Contact ,arm 71B and provides a stop for V-shaped cradle 145B.

Near the end 70B of movable contact arm 71B at which pigtail 52B is connected, an essentially rectangular section bar 180 is rigidly secured to movable contact arm 71B in any suitable way. Shaft or tie bar 180* is common to all three phases A, B and C `of the threepole circuit breaker, being rigidly secured to the ends 70 of the movable con-tact arm 71 of every phase so that one movable contact, for example 71B, is moved whether opened or closed, the other two movable contact arms 71A and 71C will `simultaneously perform the same movements. The circuit breaker is also provided, in the vicinity of arc chute 95B, with an insulation 185B for completely insulating arc chute 95B.

Thus, it will be seen that when either the time delay or instantaneous overcurrent means rotates the common tripper bar 65, in a clockwise direction, both the latch 147B and 187B will be released and hence, spring 118 will drive the contacts 77-85 to the disengaged position.

As heretofore noted this trip of the circuit breaker to the position indicated in FIGURE 2 by the release of the two latches can be achieved by either and overcurrent which will cause deflection of the bimetal 38B to 'the right and result in engagement of the adjustment screw 43B with the protrusion 66B to cause counterclockwise rotation of the tripper bar 65 or due to a fault current condition wherein the single turn of the bimetal 38B will sufficiently energize the magnetic pole 200* to thereby rotate the armature 2111 in a clockwise direction against its bias 206 thereby bringing its extension 216 into engagement with the protruding portion 60B to rotate the tripper bar in a counterclockwise direction.

Thus, it will be seen that with the novel overcurrent device of our invention, the instantaneous trip means comprising the armature 213 and the magnetic yoke 200 are mechanically independent of the time del-ay thermal means 38B and hence, the occurrence of a faul-t current or an overcurrent will result in a blow or force in one direction on the tripper bar `65 to result in the tripping of the circuit breaker.

Fixed shunt 301B is a resilient generally L-shaped member with the upwardly extending arm thereof being positioned generally parallel to the upwardly extended leg of bimetal 38B when it is not deflected. A xed shunt contact 302B is secured to the upper end of shunt member 301B and is positioned for engagement by movable contact 303B carried by the bimetal cross-mem ber 300B.

When shunt contacts 302B and 303B are engaged a complete current path between pigtails 43B and 52B which by-passes bimetal 38B is formed. This current path extends from pigtail 35B, through cross-member 300B, through shunt contacts 302B and 30GB, through low resistance fixed shunt 301B to pigtail 52B. Current flow is vshunted through this path since xed shunt 301B is of a much lower electrical resistance than bimetal 38B.

In order to prevent rebound and also to produce additional force to hold contacts 302B and 303B closed against blow olf forces due to curren-t flow through these contacts a magnetic means comprising magnet 350B and cooperating armature 351B are provided. Magnet 350B is secured to bimetal 38B by means of rivet 352B with insulating sheet 353B and other insulation (not shown) insulating magnet 350B from bimetal 38B. Armature 351B is secured to shunt 301B by means of rivet 354B and is positioned opposite magnet 350B. Iusulating sheet 355B is secured to the face of armature 351B.

Upon the occurrence of a mere overload condition the upper end of bimetal 38B will slowly deflect to the right until adjusting screw 43B engages portion 66B of tripper bar 65 and the cooperating contacts 77B, 85B

will be parted before shunting contacts 302B, 303B become engaged.

The spacing between magnet350B and armature 351B is such that the energization of magnet 350B by a fault current flowing through bimetal 38B will not attract armature 351B since instantaneous trip means 200-211 will act before any appreciable deflection of bimetal 38B.

Upon the occurrence of a short circuit or other severe fault, instantaneous trip means 20G-211 will act before screw 43B has engaged tripper bar 65. However, circuit interruption is not instantaneous so that bimetal 38B is deflected beyond the point where screw 43B engages tripper bar 65 under mere overcurrent conditions. Bimetal 38B will continue to deflect until movable shunt contact 303B engages fixed shunt contact' 302B and the major portion of the circuit current now passes through shunt 301B rather than bimetal 38B. The spacing between shunt contacts 302B `and 303B is such that they will lbe engaged before burn-out or distortion of bimetal 33B can take place.

Under these severe fault conditions magnet 350B will be sufficiently energized, even before contacts 302B, 303B engage, to attract armature 351B resulting in a more rapid closing of contacts 302B, 303B thereby reducing arcing at these contacts. Once contacts 302B, 303B are engaged, the attraction between armature 351B and magnet 350B serves to maintain contact pressure `and prevent blow-off.

In addition the utilization of the magnetic means 350B, 351B in conjunction with the bimetal shunt results in a construction Iwhere-in it is no longer necessary to compromise the rigidity of shunt 301B, as formerly required to prevent rebound, with the yieldability required to prevent bimetal distortion.

It is permissible to mount the magnet to fthe shunt and the armature to the bimetal in which event the magnetic means will not assist -the bimetal in closing the shunt circuit contacts but once these contacts engage, the magnetic means will maintain the shunt circuit closed until such time as current through the circuit breaker falls to a value which will not injure the bimetal.

In the embodiment illustrated in FIGURES 9 and l0, armature 351B of FIGURES 7 and 8 has been replaced by magnet 370B. The same reference numerals have been utilized in FIGURES 7-10 to indicate identical components.

With the arrangement of FIGURES 9 and l0, when shunt contacts 302, 303B are brought into engagement magnet 370B will be energized by the high value of current flowing through the shunt. Thus, the Iforce of tw'o magnets 350B, 370B will now act to maintain contact pressure.

In the foregoing, we have described our invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of our invention within lthe scope of the description herein are obvious. Accordingly, We prefer to be bound not by the specific disclosure herein but only by the appending claims.

We claim:

l. A circuit breaker including a pair of cooperating contacts and a bimetallic means connected in electrical series with one of said cooperating contacts; means operatively connected to `one of said cooperating contacts and actuated by said bimetallic means upon deflection thereof to a first predetermined position to thereby separate said cooperating contacts; a normally open shunt circuit actuated by said bimetallic means upon a deflection thereof to a second predetermined position; said shunt circuit when actuated being operatively connected to said bimetallic means to prevent deflection thereof beyond said second predetermined position and to provide la conductive path shunting said bimetallic means to thereby prevent burn-out and distortion thereof; magnetic means associated with said bimetallic means and said shunt circuit; said magnetic means being operatively positioned and -constructed to assist said bimetallic means in actuating said shunt circuit :and thereafter maintain said shunt circuit actuated until such time as current ow through said circuit breaker is reduced to a value which will not cause injury to said bimetal; said maglnetic means |being adapted to enable said shunt circuit to lbe rapidly urged toward said bimetal; said shunt circuit comprising la conductive shunt member; said shunt member being highly exible along its entire length to enable rapid movement of said shunt member towards said bi-rnetallic element and to eliminate contact bounce between said |bimetallic element and said shunt circuit.

2. A circuit breaker including a pair of cooperating contac-ts and a bimetallic means connected in electrical series with one of said cooperating contacts; means operatively connected 4to one of said cooperating contacts and actuated by said bimertallic means Iupon deect-ion thereof to A,a first predetermined position to thereby separate said cooperating contacts; la normally open shunt circuit actu,- ated by said bimetallic means upon a deflection thereof to a second predetermined position; said shunt circuit when actuated being operatively connected to said bimetallic means to prevent deflection thereof beyond said second predetermined position to thereby prevent burin-out and distortion thereof; magnetic means associated with said lbimetallic means and said -shunt circuit; said magnetic means being operatively positioned and constructed to assist said bimetiallic means in actuating said shunt circuit and thereafter maintain said shunt circuit actuated until such time as current flow through said circuit breaker is reduced to a value which will not cause injury to said bimetal; said bimetallic means having a first shunt contact at the free end thereof; said shunt circuit including a shunt member having a second shunt contact engageable by said first shunt contact when said bimetallic means has deflected to said second position; said magnetic means comprising a rst electro-magnet mounted to said bimetallic means and a second electro-magnet mounted to said shunt member and being energized upon the engagement of said shunt contracts; said magnetic means being adapted to enable said shunt circuit to be rapidly urged toward said bimetal; said shunt member being highly exible along its entire length to enable rapid movement of said shunt member towards said bimetallic element and to eliminate Contact bounce between said bimetallic element and said shunt circuit.

References Cited in the tile of this patent UNITED STATES PATENTS 2,322,235 Howard June 23, 1943 2,357,151 Von Hoorn Aug. 29, 1944 2,844,689 M-iddendorf July 22, 1958 2,845,507 Brumeld July 29, 1958 2,892,054 Walker et al. June 23, 1959 2,989,605 Leonard June 20, 1961 2,989,606 Walker et al. June 20, 19611 

1. A CIRCUIT BREAKER INCLUDING A PAIR OF COOPERATING CONTACTS AND A BIMETALLIC MEAND CONNECTED IN ELECTRICAL SERIES WITH ONE OF SAID COOPERATING CONTACTS; MEANS OP ERATIVELY CONNECTED TO ONE OF SAID COOPERATING CONTACTS AND ACTUATED BY SAID BIMETALLIC MEANS UPON DEFLECTION THEREOF TO A FIRST PREDETERMINED POSITION TO THEREBY SEPARATE SAID COOPERATING CONTACTS; A NORMALLY OPEN SHUNT CIRCUIT ACTUATED BY SAID BIMETALLIC MEANS UPON A DEFLECTION THEREOF TO A SECOND PREDETERMINED POSITION; SAID SHUNT CIRCUIT WHEN ACTUATED BEING OPERATIVELY CONNECTED TO SAID BIMETALLIC MEANS TO PREVENT DEFLECTION THEREOF BEYOND SAID SECOND PREDETERMINED POSITION AND TO PROVIDE A CONDUCTIVE PATH SHUNTING SAID BIMATALLIC MEANS TO THEREBY PREVENT BURN-OUT AND DISTORTION THEREOF; MAGNETIC MEANS ASSOCIATED WITH SAID BIMETALLIC MEANS AND SAID SHUNT CIRCUIT; SAID MAGNETIC MEANS BEING OPERATIVELY POSITIONED AND CONSTRUCTED TO ASSIST SAID BIMETALLIC MEANS IN ACTUATING SAID SHUNT CIRCUIT AND THEREAFTER MAINTAIN SAID SHUNT CIRCUIT ACTUATED UNTIL SUCH TIME AS CURRENT FLOW THROUGH SAID CIRCUIT BREAKER IS REDUCED TO A VALUE WHICH WILL NOT CAUSE INJURY TO SAID BIMETAL; SAID MAGNETIC MEANS BEING ADAPTED TO ENABLE SAID SHUNT CIRCUIT TO BE RAPIDLY URGED TOWARD SAID BIMETAL; SAID SHUNT CIRCUIT COMPRISING A CONDUCTIVE SHUNT MEMBER; SAID SHUNT MEMBER BEING HIGHLY FLEXIBLE ALONG ITS ENTIRE LENGTH TO ENABLE RAPID MOVEMENT OF SAID SHUNT MEMBER TOWARDS SAID BIMETALLIC ELEMENT AND TO ELIMINATE CONTACT BOUNCE BETWEEN SAID BIMETALLIC ELEMEMT AND SAID SHUNT CIRCUIT. 